The invention relates to a system for effecting data transfer between one or more objects moving along a path and one or more fixed communication stations located along said path.
Such systems are already known per se, for example from U.S. Pat. No. 5,406,275, U.S. Pat. No. 5,347,274, U.S. Pat. No. 4,501,958 and DE 4,331,286.
U.S. Pat. No. 5,406,275 describes a system that is essentially intended for detecting vehicles for the purposes of levying a toll on these vehicles as a fee for use of specific road sections. The road sections which are subject to payment of a toll are marked by communication stations which recognise passing vehicles on the basis of the identity codes transmitted by these vehicles. If the vehicles have been recognised the toll can then be levied in some way or other.
U.S. Pat. No. 5,347,274 describes a system for monitoring special transports, for example transports of chemical waste or the like. To this end communication stations are installed along the routes which the vehicles concerned have to follow. When a vehicle passes by, in any event the identity code of the vehicle is recognised in the station and it is thus established that the vehicle concerned has passed this station. In this way a vehicle can be followed and monitored over its entire route.
U.S. Pat. No. 4,501,958 describes a system that is intended for levying a toll on vehicles which make use of specific road sections. Here also identity codes are exchanged between the moving object and the fixed communication stations in order to be able to recognise the vehicles on the basis of these identity codes and to be able to levy the toll.
In all known systems a distinction is made between periods in which the distance between a moving object and a communication station is too great to be able to effect data transfer and a period in which the moving object is in the immediate vicinity of a communication station and data transfer could therefore be effected. In the first-mentioned period the transmitter/receiver combination of the object is activated in such a way that the transmitter is switched off, whilst the receiver is listening continually and waiting for receipt of an activation signal. Furthermore, the transmitter/receiver combinations of the communication stations are activated during these periods in such a way that the receiver is switched off while the transmitter is transmitting an activation signal at intervals. If one of the moving objects now comes within the range of a communication station, the receiver of this object will receive the activation signal from the station. The receiver will activate the associated transmitter, which will then transmit the identity code, stored in the identity code generator. The receiver in the station, which waits for any responses after every transmission of an activation signal, will receive this identity code and transmit it to the code recognition unit. If the code is recognised in this recognition unit, a message generator can then be activated in order to establish whether this generator contains a message intended for the object associated with this code. If this is the case, this message will then be transmitted, modulated to the activation signal or added thereto, to the moving object, where this message is received and fed to the data processing unit.
In all these known systems it is thus assumed that the moving object is in fact passive as long as no data transfer can be effected and that the fixed communication stations are continually transmitting activation signals. The Applicant has recognised that this is in fact a time-consuming system. This can lead to serious disadvantages if there is only a very limited time available for effecting the data transfer.
If the objects are, for example, moving at a speed of 360 km/h=100 m per second and if the antennas of the fixed communication stations consist of loops installed in the road surface, there being a possibility for data transfer only if the vehicle is located within a strip of, for example, 1 m, measured in the direction of movement, then there is only {fraction (1/100)} second in which to effect a complete data transfer.
It has now been found that a significant gain in time can be achieved if, in contrast to all known systems, the transmitter/receiver combinations of each moving object are continually active, at least in the vicinity of the stations, and transmit their identity codes at intervals, whilst the transmitter/receiver combinations of the stations are continually set to passive mode, that is to say the transmitters are switched off and the receivers wait until they receive an identification
In this context the invention now provides a system for effecting data transfer between one or more objects moving along a path and one or more fixed communication stations located along said path, characterised in that
each object is provided with a transmitter that is coupled to an identity code generator,
and in that each communication station is provided with a receiver that is coupled to an identity code recognition unit,
wherein the transmitter of each object is continually activated, at least in the vicinity of a communication station, such that, in an alternating series of first and second periods, the transmitter successively transmits an identity code, originating from the identity code generator, in a first period and the transmitter transmits nothing in a second period, and
wherein the receiver of each station is continually activated until an identity code is received, which code is recognised by the recognition unit.
With reference to the figures it will be explained below that a significant gain in time compared with systems according to the prior art can be achieved with this system.
In many cases the transfer of an identification code only is found to be too restricted and there is a desire to be able to transfer more data.
A preferred embodiment of the system meets this requirement. This embodiment is characterised in that each object is provided with a message generator and in that each station is provided with a message receiver,
wherein the message, always in series with the identity code, is transmitted by the transmitter of the object, and in that, in the station, which has first received the identity code, the message which follows it is passed to the message receiver and stored. In this way it is possible to transfer more data than merely the identification code between an object and a station.
A limitation to which both the embodiments described above are subject is based on the fact that transmission is possible only from an object to a station and not in the opposite direction.
An embodiment with which bidirectional transmission is possible is characterised in that, in addition to the transmitter, each object is provided with a receiver that is coupled to a message receiver,
and in that, in addition to the receiver, each communication station is provided with a transmitter that is coupled to a message generator,
wherein, after an identity code has been received in a communication station and has been recognised by the recognition unit, the message generator and the transmitter are activated in order to transmit any message intended for the object concerned and
wherein the receiver of each object is ready in each second period to receive any responses and pass these to the message receiver.
Bidirectional traffic is possible with this embodiment. A disadvantage is still lurking in the fact that less time is available for transmission of a message from object to station than in the opposite direction because some of the available time has to be used for transfer of the identification code.
An embodiment that does not have this disadvantage is characterised in that each object is provided with a message generator coupled to the transmitter and in that each communication station is provided with a message processing unit coupled to the receiver, wherein, after the message receiver in the object has received, or after a predetermined waiting period following the transmission of the identification code, the transmitter and the message generator in the object are activated in order to transmit any message
and the receiver in the station, after transmitting a message to the object, or after receipt of the identification code, waits for any message from the object.